The present invention relates generally to utility poles that are capable of absorbing impact energy, as from a motor vehicle collision, thereby reducing the effects of the impact on the vehicle and its occupants. The utility poles of the present invention are constructed so as to enable ease of conversion and replacement of currently installed poles.
Wood, specifically tree trunks impregnated with creosote and other chemicals, is currently the most widely used material for utility poles. It is estimated that at least 114 million wooden poles are currently in service in the United States alone. A wooden pole is very durable, nonconductive, and amendable to a wide variety of methods for attachment of overhead wires. One of the major advantages of wooden poles is the low cos:t of the basic pole, approximately $250 for a 40-foot tall, 11-inch diameter Class 3 pole. In addition, wooden poles are well understood by utility companies and other users of pole-supported systems, and are accepted by the general population as a necessary component of various wire and cable distribution systems.
However, wooden utility poles do have several drawbacks. First, wooden poles must be chemically treated to prevent insect attack, a process that creates both current problems with hazardous material disposal at the manufacturing site and future problems with disposal of the treated poles once they are taken out of service. Second, the chemical treatment does not guarantee that the pole will not be damaged by insect attack or rot, another major contributing cause of pole failure. Third, the weight of a wooden pole can complicate installation in areas that are not easily accessible for truck-mounted cranes and other installation equipment. Finally, one of the major problems with wooden utility poles is their unforgiving nature when they are involved in a vehicle accident.
United States Department of Transportation (DOT) regulations require that most roadside equipment be designed to have breakaway or other safety features that limit vehicle decelerations caused by impact with the equipment in an accident. However, wooden utility poles are one major exception to this rule, primarily because no technically and economically viable alternative to the wooden pole has been identified.
Although some investigation of methods for incorporating breakaway features into wooden pole designs have been conducted in the past, the expense associated with the incorporation of breakaway devices into wooden poles has prevented the widespread application of this technology. In addition, it is not obvious that a breakaway pole made from any material would significantly increase the overall public safety. It can be argued that a vehicle that passes through a breakaway pole with minimum deceleration is very likely to impact a tree, building, or other less forgiving obstacle a short distance past the xe2x80x9csafexe2x80x9d pole, while still moving at considerable speed.
DOT has postulated that a much more desirable and safer system would involve a utility pole that could bring a vehicle to a stop by collapsing in a controlled fashion during an automobile impact, or at least could safely remove a significant portion of the vehicle""s energy during its dynamic interaction with the pole. A steel luminaire having these general characteristics has been demonstrated in Sweden. However, the cost of manufacturing such poles, and their conductivity, make their widespread use, particularly to carry overhead wires, impractical.
Thus, use of more modem composite materials in place of wood or steel to produce energy-absorbing utility poles is highly desirable. Composite materials have already proven to be capable of making technically-acceptable utility poles that meet normal day-to-day operational requirements. However, current composite poles act as breakaway devices rather than energy absorbing devices. Thus, current composite poles do not provide the safety features desired during a vehicular collision.
The potential market for repair/replacement poles is very large. It has been estimated that approximately 4% of the installed poles, or 4.5 million units, are replaced annually. If the approximate retail cost of a replacement composite energy absorbing pole were as little as $300 each, then this market would exceed $1.35 billion annually. To date, that market has not been developed. Composite poles are currently used in special applications that can justify their higher installation cost, as compared to wood. However, because composite poles made using current technology are generally two to four times more expensive to purchase than an equivalent wood pole, the market acceptance of composite poles has been greatly limited.
For these reasons, the ideal utility pole would possess the following general characteristics. First, it should have the ability to absorb impact energy and induce the safe deceleration of an impacting vehicle while greatly reducing the existing velocity of the vehicle, as compared to a breakaway design. Second, it should be manufactured from nonconductive material suitable for use in carrying utility wires. Third, it should be able to be produced, installed, and maintained at a cost that encourages utility companies to employ the new pole technology as the standard equipment. Fourth, it should be capable of being used as a replacement component of a composite/wood hybrid pole. Fifth, it should reduce the problems associated with hazardous material disposal both during manufacture and on later disposal of the spent equipment.
Accordingly, it is an object of the present invention to provide a utility pole that is capable of absorbing impact energy and inducing a safe deceleration of an impacting vehicle, as compared to a breakaway design.
It is another object of the present invention to provide a utility pole that can be produced, installed, and maintained at a cost that encourages utility companies to employ the new pole technology as the standard equipment.
It is a still further object of the present invention to provide a utility pole that capable of being used as a replacement component of a hybrid pole.
It is yet another object of the present invention to provide a utility pole that reduces the problems associated with hazardous material disposal both during manufacture and on later disposal of the spent equipment.
The present invention provides energy-absorbing utility poles and replacement components. In one embodiment, the poles of the present invention are designed to bring an impacting vehicle to a controlled stop. Analysis of crash energetics in combination with proven energy absorption capacities indicate that composite pole weights of between 100 and 400 lbs. For a twenty-five foot long replacement pole should provide safe vehicle stops for a wide range of vehicle encounters (1800 to 3600 lbs. at 60 mph).
In a further embodiment, the poles of the present invention are capable of use as a field-replaceable component for an existing, damaged wooden pole to form a hybrid pole system. In this embodiment, a previously installed but damaged conventional wooden pole may be sectioned below the lowest overhead service attachment to form an upper and a lower section, with the old upper wooden section being retained with all previously attached hardware and inserted into a new lower section comprising a pole of the present invention in combination with a slip joint or permanent connection.
In a new installation, this wood/composite hybrid can be assembled offsite at a factory and installed just like a conventional new pole.
In one embodiment, the products of the presently claimed invention are formed using a pultrusion process that result in a pole having low to moderate diametric crush strength so as to initiate a flattening and then folding response as the vehicle encounters the pole. The pultrusion process comprises a wet bath resin impregnation of a fiber preform incorporating reinforcing materials (dry unidirectional fibers, cloth, multi-axial stitch bonded materials, braided preforms, and specially produced 2D and 3D reinforced materials) that are continuously pulled from spools or woven in-line prior to being passed through an optional preheating furnace, which dries the materials and improves resin wet-out, and then passed through several forming cards before introduction into a one-meter long heated steel die, which compacts the material into the final geometry against a cantilevered, free-floating mandrel. In an optional embodiment, the liquid resin matrix may be injected directly into the die.
Pultrusion differs considerably from filament winding technology used by current producers of composite poles. Most significantly, pultrusion can make poles as a continuous stream as quickly as 3 feet per minute. In comparison, other composite pole manufacturing systems make poles one at a time, requiring much greater labor input, larger capital investment, and longer processing time and producing much more scrap.
The utility poles of the present invention may be made either as stand-alone units or as replacement components, wherein a damaged existing pole would be sectioned below the lowest service attachment, forming a lower, damaged section and an upper, functional section; the lower, damaged section removed and replaced with a pole base component of the present invention; and the upper, functional section of the original pole assembled with the replacement base component. An advantage of this operation is the ability to retain intact all of the service connections to the upper section of the damaged pole during the transfer to the replacement pole base. This eliminates the need for multiple visits by the various utilities using the pole to transfer the wires from the damaged pole to the replacement pole. Typically, the upper section of the damaged pole is secured to the bucket of a bucket truck: prior to sectioning the damaged pole and then released once the upper section is attached to the replacement pole.